Early Life Stage Mortality Syndrome in Fishes of the Great Lakes and Baltic Sea

<em>Abstract</em>.—The carotenoid levels in Baltic salmon <em>Salmo salar </em>appear to have decreased as the incidence of the M74 syndrome has increased during the last 20 years. Our preliminary investigations suggested a relationship between a low level of the carotenoid astaxanthin in yolk sac fry of Baltic salmon and elevated mortality attributable to M74. The objective of this study was to further detail this relationship during the spawning seasons of 1994 and 1995 in salmon taken from hatcheries on the Baltic Sea, the Swedish west coast, and Lake Vänern. Total carotenoids and astaxanthin were measured in female muscle tissue and eggs. The carotenoid concentration and the ratio of astaxanthin to total carotenoids were significantly lower in the muscle of Baltic salmon females than in the muscle of feral females from salmon stocks on the Swedish west coast and in Lake Vänern. A relationship between low muscle levels of astaxanthin in Baltic salmon females and M74 in the progeny was observed, and yolk sac fry from eggs with low astaxanthin content tended to exhibit M74 more often than fry from eggs with high astaxanthin concentration. The low levels of astaxanthin observed in Baltic salmon eggs and yolk sac fry may be part of a general astaxanthin deficiency in the feral Baltic salmon.